At the highest level, the heart is responsible for moving oxygen poor (blue) blood to the lungs via the right ventricle through the pulmonary artery to the lungs, where capilaries infuse the blood with oxygen (it becomes red) and is then sent through pulmonary veins to the left ventricle where it is pumped through the body. The body uses the oxygen, the blue blood returns to the right side of the heart, is oxygenated by the lungs, becomes red, pumps to the left side of the heart and so on. The US Department of Health and Human Services has a great webpage dedicated to "How Your Heart Works" if you're interested in gaining a high level, but still detailed overview of the organ that is in charge of operating the body's circulatory system.
In Luke's specific defect, Atrioventricular Canal Defect or AV Canal for short, there are a number of structural problems present. He has a hole between the top two atrial chambers known as an Atrial Septal Defect or ASD. He also has a second hole between the bottom two ventricular chambers known as a Ventricular Septal Defect or VSD. Additionally, he has one valve that we refer to as a "common mitral valve" that in a normal heart would be referred to as two separate valves, a Tricuspid Valve that would connect the right ventricle's atrial and ventricular chambers and a Mitral valve that would connect the left ventricle's atrial and ventricular chambers. In an AV Canal defect, The ASD is placed towards the bottom of the atrial chambers and the VSD is placed towards the top of the ventricular chambers so they end up meeting in the middle to create one large 2D hole in the middle of the heart, which when combined with the common mitral valve creates a 3D hole that connects many various components. As a result of this anatomical defect, some of the oxygenated or red blood in the left ventricle that has just come from the lungs and is ready to be circulated throughout the body ends up passing across the VSD and mixing with the blue or de-oxygenated blood creating a right to left shunt. (My understanding is that the left to right shunt creates a loud "wooshing" sound - a murmur that is heard with a stethoscope). The extra volume or blood pressure in the right ventricle, if left uncorrected - over time cause will cause the ventricle to become enlarged which is considered to be irreversible damage. Because there is now extra blood in the right ventricle and it has to go somewhere, it passes through the pulmonary artery to the lungs, where pulmonary hypertension is often detected due to the increased volume of blood present there. Over time, again - left uncorrected, the lungs will become enlarged which is also considered irreversible.
Individuals with this defect typically undergo open heart surgery to repair the defect between two and six months of age due to failure to thrive/poor weight gain as the body burns more calories than it consumes because the heart has to work so hard to pump blood and / or because of poor oxygenation due to the shunting which causes the skin to be gray, blue or purple. In Luke's case we are waiting until he is 16.5 months old for the repair based on the findings of a heart catheterization that was performed when he was four months old. We learned during that procedure that an unusual piece of cardiac tissue grew up to cover a portion of his VSD so blood flowing across that area of the defect is less than you'd expect, which helped us to understand why he wasn't showing the clinical signs of heart failure - failure to thrive and / or poor oxygenation. To repair the ASD and VSD, our surgeon will patch each of the holes with a synthetic material. Additionally, Luke's heart isn't equally balanced - typically, the right and left ventricles should be the same size, but his heart has a mild to moderate right ventricle dominance (which for a period of time prenatally had us worried that we'd have to do a single ventricle repair of his AV Canal, which would be much less than ideal). The right ventricle dominance becomes important when considering the common mitral valve that will be split into two valves as it will have to be split in equal proportion to the sizes of each side of his heart. I recently learned that this becomes even more complicated for Luke because the papillary muscles that are responsible for contracting during systole to prevent regurgitation of blood into the atria and that line the exterior of the common mitral valve are placed very close together. These are the muscles that will attach the valves to the correct chambers of the heart during the repair and they will have to be separated when the valve is split. This will require a very steady hand to be done correctly.
Some other details we have recently learned are included below:
- Nutrition is key leading up the surgery and we are starting him Pediasure immediately for the calories to help him gain weight and protein for it's vital role in healing muscles.
- We are planning to be in Boston for 10-14 days for the repair - this is extended from the orignal expectation of 7-10 days because of Luke having laryngomalacia, which complicates the extubation process
- It is highly likely that there will either be some leakiness or some stenosis or possibly both following the repair - the goal is that it's minor
- The heart is living tissue that will continue to evolve after the repair. It will likely be years before we are aware of any possible muscle/valve deterioration, including leaky valves or valve stenosis.
- In general, individuals with DS are at a greater risk of pulmonary hypertension over the course of their lifetime due to the combination of poor muscle tone and anatomically small airways - this can be a major contributor to an increased number of respiratory issues and is something we will always have to monitor very closely.
- We expect for surgery to last 6-8 hours, although 8 hours is on the long side - this will include the time it takes to get him under anaesthesia.
- Following the surgery, the surgeon will come out to talk with us and we can expect to see Luke an hour to an hour and a half afterwards.
- There are extrordinary precautions taken in the OR and CICU to mitigate infection including sterile environments and repeated handwashing. Infections are a huge quality metric for the hospital and something they take very seriously.
- We should expect for Luke to come out of the OR with a fever and to have a fever for some period of time following the surgery. This is normal because during the surgery while Luke is on the heart/lung bypass machine, his white blood cells will come in contact with the plastic tubing within the machine and they will tell his body that the plastic is a foreign object - his body will respond as if it's fighting off the foreign object and a fever will ensue.
- Following the surgery (while still in the hospital or shortly following discharge), minor infections like ear infections and tracheitis are fairly common. That said, major infections like those of the breastbone and around or in the heart are very rare as a result of the surgery.
- Luke will receive blood products/transfusion during the operation and we will need to validate that he doesn't become immune to the Hepatitis A vaccination following the repair. If this is the case, he could have an adverse reaction to the vaccination that will be due for him at his 18-month well child checkup with the pediatrician.
- Average total recovery time is about 8 weeks. Once we are home from Boston, Luke will need to be isolated as much as possible from other people / germs for at least 4 weeks.